Copyright Statement

Abstract

In the 2 years that followed the 100-year flood incident of September 1986 in the Saginaw
River/Bay ecosystem, the reproduction of Caspian terns collapsed and then slowly recovered. Egg viability
and fledging rates of hatched chicks were drastically depressed in 1987 and 1988. Eggs from clutches
laid later in the year were less viable and chicks hatched from these eggs displayed wasting syndromes
and deformities. The post-flood rate of deformities in hatched chicks in 1987-1989 was 163-fold greater
than background rates for this population in 1962-1967. Embryonic abnormalities and deformities were
found in many embryos recovered from dead eggs. Recently published data on planar toxic chemicals
from samples of forage fish, tern eggs, and chicks from water birds nesting in the bay implicate planar
dioxin-like PCBs 77 and 126 as the sources of these severe bioeffects. The planar PCB congeners
accounted for >98% of TCDD-EQ toxicity in the tern eggs, and several were present at levels near or at
the LD95 levels each for chicken eggs. Actual TCDD was about 1% of the TCDD-EQ toxicity. Very rapid
buildup rates of PCBs were measured in tern eggs. The calculated toxic potency of PCB recovered from
tern eggs was about 15-fold greater than parent aroclor 1242 PCB. Smaller tern species were projected
to be much more at risk than the larger Caspian tern due to greater standard metabolic rates. The study
supports the view that sediment disturbance and sediment banks of toxic chemicals are major threats to
upper trophic level fish-eating species.